The use of thermoplastic roll wrap films for protecting goods, and in particular, large paper roll stock is a significant commercially important application of polymer film, including generically, polyethylene. However, a factor affecting their acceptance is the machine performance of the roll wrap films.
In one commercial application, roll wrap film of the present invention is used as primary protection of a mill roll of fine paper. In this application, the roll wrap film is typically applied in multiple layers around such fine paper. These rolls of fine paper typically include bar codes which contain information such as product type, purchase order number and weight. Roll wrap film may be applied in conjunction with pre-stretch machines and non pre-stretch machines. The use of a pre-stretch machine tends to cause severe "tiger striping" in many roll wrap films because of the lack of uniform stretching.
Tiger striping is a condition in the stretched films where bands or patterns across the films have not been stretched as compared to a remainder of the roll wrap film. This condition is caused by the high strain on the stretched roll wrap film. This non-uniform stretching results in a "wrinkling" pattern in the roll wrap film which can cause distortion in the scanned reading on the above-described bar codes. In addition, the tiger-striped film has less effective cling properties and may even cause damage to the wrapped product.
Some of the properties desired of a good roll wrap film are as follows: good cling or cohesion properties, high puncture resistance, good machine direction tear resistance, good transparency, low haze, low stress relaxation with time, high resistance to transverse tear especially when under machine direction tension, low specific gravity and thus high yield in area per pound, good tensile toughness, high machine direction ultimate tensile strength, high machine direction ultimate elongation, and low modulus of elasticity.
A need exists to develop superior roll wrap films having excellent machine performance with excellent stretched clarity and uniform stretched gauge, while still maintaining other important roll wrap film properties.